This invention relates to a sheet media handling system and a printer having the same for supporting both small and large width sheet media. More particularly, this invention relates to a sheet media handling system and printer having the same for presenting a large width sheet medium, that is partially supported by a stack of small width sheet media, substantially aligned to an infeed zone of the printer.
Office equipment such as photocopiers, laser printers, ink jet printers and other imprinting mechanisms today incorporate an ability to receive sheet media from any one of two or more trays. It is very common to have a bypass tray in which a single sheet medium of a special type or of a different size can be conveniently fed for particular printing without having to load it onto pull-out trays.
FIG. 1A shows one prior art media handling system having a pressure plate pivotably mounted on a base of a printer. During a pick cycle, the pressure plate is lifted to move a stack of sheet media located above it to an infeed zone of the printer. This pressure plate is usually designed to directly support a stack of sheet media in a main tray. During each pick cycle, the sheet at the top of the stack will be moved to the infeed zone. A simple and economical design of a bypass feeding system usually has a bypass tray positioned above the main tray. Sheet media in this bypass tray is supported either by the pressure plate itself (when there is no sheet medium in the main tray) or by a stack of sheet media in the main tray as shown in FIG. 1A. Such a design accords pick priority to any sheet medium in the bypass tray over that in the main tray. This design works well when the sheet media on both the bypass and main trays are of substantially the same width. When the media are of substantially the same widths, the sheet media in the main tray will be able to provide sufficient support for the sheet media in the bypass tray.
However, a serious problem results when the sheet medium in the bypass tray is substantially wider than a stack of sheet media in the main tray. For example, the sheet media in the bypass tray is of B4 size and the sheet media in the main tray is of A4 or Letter size. A substantially large portion of the B4 size sheet medium in the bypass tray will not be supported by the A4 or Letter size sheet media in the main tray. The problem is not so serious when there is only a small stack of sheet media in the main tray. A small stack will create only a small height differential between portions of the B4 size sheet medium. In such a case, the B4 size sheet medium is still fairly well supported, partly by the stack of sheet media in the main tray and partly by the exposed portion of the pressure plate. As a result, the B4 size sheet medium can be properly presented for picking by the pick mechanism in the printer.
However, when the stack height of the smaller width sheet media in the main tray measures half an inch or more, a relatively large portion of the B4 size sheet medium would not be supported by the pressure plate and would sag at the arris of the stack of sheet media in the main tray as shown in FIG 1A. Such sagging is detrimental to the aligned feeding of the B4 size sheet medium into the printer as the sheet medium will not be properly presented to the pick mechanism. The pick mechanism is only able to properly engage the portion of the B4 size sheet medium that is supported by the stack of sheet media in the main tray as shown in FIG. 1B. As a result, the properly engaged portion will be drawn into the printer ahead of the rest of the sheet medium. Such an action would cause the sheet medium to follow an oblique course or a deviation from a predetermined straight line path when being received into the printer. Such unbalanced drawing in of the B4 size sheet medium results in skewing of the sheet medium. This skewing causes undesirable result, for text printed on the skewed sheet medium will appear misaligned, crooked or oblique. In some cases, when the skew is severe, the sheet medium may end up jamming the printer.
A two-part pressure plate disclosed in the U.S. Pat. No. 6,152,440 can be used to overcome the problem of unbalanced support or sagging of the B4 size sheet medium. The pressure plate includes a primary pressure plate for supporting media in the main tray and a secondary pressure plate that is raised to support portions of a larger width sheet media that is not supported by media in the main tray. The secondary pressure plate is actuated by a mechanism that is responsive to a media guide used to align a stack of sheet media in the main tray. Although such a design works well, it is not possible to implement the mechanism where space is a constraint. The secondary pressure plate is also inoperative if a user forgets to move the media guide into position against the stack of sheet media in the main tray.
According to an embodiment of the present invention, there is provided a sheet media handling system suitable for use with a printer. The sheet media handling system includes a first support and a second support adjacent the first support. In use, the first support supports first sheet media and second sheet media on the first sheet media. The second support supports a portion of second sheet media that is not supported by the underlying first sheet media. A biasing means biases the second support. The biasing means is collapsible under the portion of up to a predetermined number of sheets of the second sheet media. During a pick cycle when the first support is moved to present supported media thereon to an infeed zone of the printer, the portion topmost of the second sheet media is brought to within a predetermined tolerance of the infeed zone.
Further according to the embodiment of the present invention, there is provided a printer that includes the above sheet media handling system.